Add travis CI config

scripts/travis-build.sh

Index: scripts/travis-build.sh
diff --git a/scripts/travis-build.sh b/scripts/travis-build.sh
new file mode 100755
index 0000000000000000000000000000000000000000..6f34d7e6df41786545a523b1c502a7bc5f0861dd
--- /dev/null
+++ b/scripts/travis-build.sh
@@ -0,0 +1,15 @@
+#!/bin/sh
+
+set -ex
+

[vapier, 2016/04/11 15:09:17]

i would restructure this code a bit up front:

 setup_env() {
   ... mess with cc/cxx ...
 }

 build() {
   ./configure
   make ....
 }

 main() {
   setup_env
   build
 }
 main "$@"

[Ted Mielczarek, 2016/04/11 16:30:18]

Okay. I'm not a big fan of overly-complex shell scripts (I generally move to
Python for anything that winds up non-trivial), but I don't care too strongly
about it in this case.

+if test -n "$USE_CC"; then
+  export CC=$USE_CC
+fi
+if test -n "$USE_CXX"; then
+  export CXX=$USE_CXX
+fi
+
+# Use -j4 for faster builds. Travis build machines under Docker

[vapier, 2016/04/11 15:09:17]

i've never run into this problem.  i do:

 ncpus=$(getconf _NPROCESSORS_ONLN)
 make -j${ncpus}

we should at least calculate the value dynamically rather than hardcode 4

[Ted Mielczarek, 2016/04/11 16:30:18]

I tried something very similar:
https://github.com/luser/breakpad/commit/ab5619c5250cb5f0f3a785c107ecf841afff...

which made the build use `make -j32`, and it resulted in my GCC processes being
killed (presumably by OOMkiller):
https://travis-ci.org/luser/breakpad/builds/120983550
This is definitely a hack, but given that it's written to run only in the Travis
environment it doesn't bother me overmuch. If I made it `min($ncpus,4)` would
that be better?

+# have a lot of cores, but resource limits will kill the build
+# if we try to use them all.
+./configure && make -j4 check